Dashboard - Adjusting gauges and estimating MPG

Jonboat2Bassboat

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Jul 27, 2012
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The Faria analog Tilt/Trim gauge does not start moving until the outboard is 1/4 way down and stops 1/4 way from the end. My guess is there is an adjusting screw on the back that lets the tilt indicator be set to the bottom when the engine is all the way down, correct?

The Faria analog speed gauge does not work all the time. Sometimes, but not always, it does not register until going 15+ MPH, jumps to current speed and then works fine. My guess is there is an air leak in the vacuum line, most likely at the gauge or manifold ends and clipping off a 1/4" at both ends will fix the problem. Either that or the gauge is dirty internally and needs to be taken apart and cleaned or replaced. Am I on the right track?

Estimating MPG. I have a trip planning program that includes fuel use. The default value is 6.5 MPH / 2.5 gallons. That's 2.6 MPG, WAY too high fuel use. Any guess as to what an 1800 pound 18 foot aluminium bass boat with a 70 HP 4 stroke Yamaha would get at a nominal speed of 10 MPG?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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the speedometer is a pitot tube type, clean the tube and pickup. if that doesn't work, the gauge bourdon tube may be tweaked

if you want 10mpg in a boat, add a sail or a dozen slaves with oars like the vikings did

2.6 mpg is not bad. best your going to get is maybe 5 miles per gallon, and that is with the wind and current at your back.

idling along will get you the most fuel economy, however take a month to get anywhere

fuel economy and boating are two different things.
 

ondarvr

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My answers

The trim gauge is of little value, I've never used one on an outboard, nor have I ever wanted or needed to.

​The pitot tube type speedometer is about in the same category, they don't work well at lower speeds and are marginal and untrustworthy at higher speeds. Get a GPS/FF combo.

​If you really want to get the best MGP possible, 10MPH is about the worst speed to find it, you need to be going slow at an idle, or on plane and in the sweet spot. The only way to find the best cruising speed is to use a fuel flow monitoring system, there's few out there, but probably not worth the expense for a boat like this one.
 

dingbat

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Nov 20, 2001
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My trim gauges hasn't worked in years. Wouldn't use it if it did. Trim to right running angle by sound and feel.

Don't have a speedometer. Use combination of gps and paddle wheel speed sensor (trolling).

Running computerized fuel flow system. When flat, I get 1.9 mpg @ 27 kits. Throw in some wind, wave and tide that number drops to 1.2 - 1.4 mpg @ 20 kts.

Have experienced less than 1 mile per gallon performance a couple times under adverse conditions.

Maybe why I have 149 gallon fuel capacity on a 22' boat....lol
 
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oldjeep

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May 17, 2010
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My trim gauges hasn't worked in years. Wouldn't use it if it did. Trim to right running angle by sound and feel.

Don't have a speedometer. Use combination of gps and paddle wheel speed sensor (trolling).

Running computerized fuel flow system. When flat, I get 1.9 gpm @ 27 kits. Throw in some wind, wave and tide that number drops to 1.2 - 1.4 gpm @ 20 kts.

Have experienced less than 1 mile per gallon performance a couple times under adverse conditions.

Maybe why I have 149 gallon fuel capacity on a 22' boat....lol

1.9 gallons per minute? ;).
 

JimS123

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None of my outboards have trim gauges and I don't need one since I can see the engine. However, my I/O has one and its an invaluable tool. When I go over sandbars or the shallows I know exactly when the prop is above the bottom of the boat. Without the gauge I would undoubtedly have hit the bottom more than once.

My OEM pitot tube speedometer agrees with my GPS and paddlewheel within 1 mph. When it doesn't I clean and/or replace the pitot, and of course check that the tube is air tight. It's been working fine for 33 seasons now.

My Mercury 4-stroke's sweet spot is 4000 rpm and gets 8.43 mpg at 19.4 mph. The only spot better than that is at 1500 rpm, which equates to 4.5 mph and 11.25 mpg. My boat is a little lighter than yours, and of course the motor is smaller as well. I would guess you could hope for about 6.5 mpg optimum.

For your Yami I would consider about 2/3 of the max rpm to give the best economy. 10 mph won't cut it, and it wouldn't meet a no-wake zone either.
 

Silvertip

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To get a better idea of what fuel consumption is, go the Yamaha web sit and check the tab that says PERFORMANCE BULLETINS. Select the engine you have, select the boat you have (or one similar to it) and then all the performance and fuel consumption data is shown. I ran a check for you and the sweet spot is about 4.5 MPG. And as is true for most outboards (4-stroke or not) you can use the 10% rule for fuel economy. That's 10% of rated horsepower at wide open throttle. 50 HP = 5 gph, 70 HP = 7 gph (actually 6.4 gph for the combo I looked up which was a couple hundred pounds lighter than your rig).
 
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Jonboat2Bassboat

Petty Officer 3rd Class
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Jul 27, 2012
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Sorry, meant what MPG to expect at 10 MPH, not MPG. Are there boat speedometers with an odometer? I have only seen them with an hour indicator.

The pitot pickup opening on the outboard is clean but there may be some obstruction further up the tube. Will try to blow out and cut back the tube ?? at the gauge end. When the speedometer works it agrees with the GPS speedometer on the chartplotter. I am selling the boat and want all the gauges to work if possible.

As for trimming an outboard to the right running angle by sound and feel, what am I listening and / or feeling for?

Thanks Silvertip, will look up the boat / engine combo. Jumping from 2.6 MPG to 4.5 or better at 6.4 would be great news. Will pay attention and see what the actual MPG is.
 

NYBo

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The trim gauge on my pontoon boat is going in the trash when I pull the boat out this fall. Useless (or would be even if it worked).
 

Jonboat2Bassboat

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Jul 27, 2012
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Thanks Silver Tip,

Looked up Yamaha performance.The chart of the 3 speeds I typically run at show much better MPG than 2.6.
Will pay attention to boating miles and fuel use to see what actual MPG is.


PERFORMANCE DATA
Yamaha 70 HP 4 Stroke ? Polar Kraft Aluminium Bass Boat 1800 Pounds

RPM MPH GPH MPG
2000 6.4 0.9 7.11
2500 8.3 1.4 5.93
3000 13.1 1.8 7.28
 

Stumpalump

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Dec 5, 2013
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Not sure on your Yamaha but most trim gauges have a sensor potentiometer on the engine that is adjustable. When they do work it's nice to just trim up to a known good point and tweek it from there. My boat never came with a guage so I trim by feel. You want it down for take off then you trim up until it steers lighter and the rpm come up. Too high and the bow will bounce and or if way too high it will allow the prop to ventilate to air causing an over rev. Bring it up on plane and work your trim up to slow so the trim raises RPM. When it stops raising RPM then stop trimming up. Get to your cruise RPM for best milage ( probably 4300-4800) and just bump the trim until it just stops increasing RPM at that particular throttle setting. That's you best trim and Max efficiency. Your trim guage is worthless to get you to the sweet spot but good at remembering about where that is. Wind and load affect trim so bump it up and down often to keep the RPM's up. I'm also in an 18' aluminum boat and will run 130 miles this weekend so max fuel range will be insured with constant trim tweeks. I'll burn 20 gallons at best but will have 28 on board. Your speedometer is old school junk. Use a phone app, GPS or fish finder with MPH on it instead. You can also fool with trim for max MPH at a given throttle setting. That will be max efficiency as well. Good luck on your trip!
 

JASinIL2006

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Trim gauges are particularly handy if you boat much in skinny water. Nice to know where the drive is...
 

JoLin

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10 MPH? Is your boat even planing at 10 MPH? 10 MPH is typically a speed at which the hull is pushing a lot of water instead of riding on top of it. Fuel economy suffers big time.

My .02
 

QBhoy

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I've never seen a water pressure speedo working below 10/15 mph.
Also. As mentioned that isn't a good speed for economy. Best economy is likely just above tick over at about 1000 rpm and just above planing speed and well trimmed...probably about 20-25mph....as a rough guide.
 

JimS123

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Are there boat speedometers with an odometer? I have only seen them with an hour indicator.
I have an Eagle Sonar Unit with a Paddle Wheel speed sensor. It has an odometer readout. However, it resets to zero when you turn it off. I use it to see how far we went on any given outing.
 

JoLin

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I have an Eagle Sonar Unit with a Paddle Wheel speed sensor. It has an odometer readout.

Should be good enough for guesstimating purposes. Probably puts you in the ballpark, but of course current will have a big effect on it. My chartplotter has two 'trip odometer' options thta I've used to zero in on my consumption over a couple of long (app. 250 miles) summer voyages. I plan my fuel stops now based on an average of 1.1 MPG :facepalm:

My .02
 

Jonboat2Bassboat

Petty Officer 3rd Class
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Jul 27, 2012
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Thanks Stumpalump,

Will save advice and use next boating season. Had a 16 foot Jon boat w/ 40 HP Yamaha (no gauge) and could trim by sound and feel. Don't seem to be able to it w/ 18 foot bass boat and 70 HP Yamaha. Looking for bigger boat w/ 115 to 150 OB and trim by RPM will help a lot.
 
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